Abstract Establishing proper retinal circuitry remains a central issue in visual system development. How neurons find their correct target remains largely unknown. The first synapse in the retina provides a simple and experimentally tractable system to explore the basis of synaptic specificity. Rod and cone photoreceptors synapse selectively with rod bipolars and cone bipolars, respectively. To identify the molecular mechanism mediating specificity, I generated transcriptome profiles of the different photoreceptors and their corresponding bipolar cell targets during synaptogenesis. From these data sets, I find distinct transcripts encoding cell surface and secreted proteins as promising candidates for this process. Using in vivo genetic manipulations and developmental approaches, I will assess the function of these genes in establishing proper connectivity. From my initial screen, I find the following: 1) non-canonical Wnt signaling between rods and rod bipolars is responsible for dictating the position of the synaptic layer, 2) Rspo2 in rods is involved in layer segregation, and 3) Nrcam in cones mediates selective connectivity to cone bipolars. I subdivided this proposal into two parts where I study rod-to-rod bipolar connectivity in Aim 1 and address cone-to-cone bipolar connectivity in Aim 2. The first section of each aim involves expanding on my preliminary findings and will be completed in the K99 phase. The second part involves continue screening and expanding on the new phenotypes which will be initiated under the mentorship of Dr. S. Lawrence Zipursky and will be completed during the R00 phase. This project has been designed to facilitate Dr. Zuniga-Sanchez to obtain a position as a tenure-track Assistant Professor at a top-tier academic research institution. With the help of her mentor and Advisory Committee, she has generated promising data and made significant progress on her research. As an independent investigator, she plans to continue her work studying the development of the mammalian retina with a clear relevance to human health. During the K99 phase, she will continue benefiting from the mentorship on the developing visual system from Dr. Zipursky. She will also receive additional career and scientific guidance at regular scheduled meeting and presentations with her Advisory Committee. Dr. Zuniga-Sanchez will participate in career development workshops offered through UCLA in preparation to apply for faculty positions and transitioning to the R00 phase. This grant proposal outlines the training, resources, and network of collaborations needed to establish Dr. Zuniga-Sanchez as an independent investigator in the vision field.